This proposal represents a multinuclear, multifield, and multiphase investigation of the metal sites in metalloproteins. The primary nuclei to be examined in this research are 113Cd, 67Zn, and 95Mo. Much of the proposed research is a continuation of a successful research program in 113Cd NMR spectroscopy. The experiments include single crystal experiments on new model compounds for the active site o carboxypeptidase and continued work using Cd2+ as a prosthetic spin-spy in protoporphyrin dependent protein, i.e. hemoglobin and chlorophyll. However, several new experiments are proposed. These include dynamic angle spinning (DAS) experiments which will average the second order quadrupole broadening to zero. A primary objective of the experiments, cross-polarization in combination with DAS, is to make the observation of quadrupolar nuclides (67Zn and 95Mo) in metalloproteins a practical experiment in the solid state. Such experiments, if proven successful, would provide a much needed direct spectroscopic approach to study the structure and bonding in this important class of metalloproteins. Further, results from such research will provide independent collaboration of the results based on the surrogate probe strategy, i.e. 113Cd nmr of those proteins where the Zn2+ ion has been replaced by Cd2+. Further, it is demonstrated that ab initio MO calculations of metal ion shielding tensors are consistent with our simple "shielding rules". These rules came about as a result of our single crystal experiments. Based upon these results, we will also utilize these calculations as a guide to interpret our protein data.